Rip out the _preUpdate handling, it's complicated and messy to maintain

module/documents/Actor.mjs

@@ -1,4 +1,5 @@
 import { __ID__ } from "../consts.mjs";
+import { clamp } from "../utils/clamp.mjs";
 
 const { Actor } = foundry.documents;
 const { deepClone, setProperty } = foundry.utils;
@@ -28,7 +29,30 @@ export class TAFActor extends Actor {
 	// #endregion Lifecycle
 
 	// #region Token Attributes
+	/**
+	 * @override
+	 * This override exists in order to support making updates to the Actor's
+	 * embedded attribute Items from the token, or falling back to the default
+	 * handling if it's not one of our attributes.
+	 */
 	async modifyTokenAttribute(attribute, value, isDelta = false, isBar = true) {
+		if (attribute.startsWith(`attr.`)) {
+			const key = attribute.slice(5);
+			const attr = this.getAttribute(key);
+			value = isDelta ? attr.system.value + value : value;
+			value = clamp(attr.system.min, value, attr.system.max);
+			const updates = { system: { value } };
+
+			const allowed = Hooks.call(
+				`modifyTokenAttribute`,
+				{ attribute, value, isDelta, isBar, isEmbedded: true },
+				updates,
+				this
+			);
+
+			return allowed !== false ? await attr.update(updates) : this;
+		};
+
 		const attr = foundry.utils.getProperty(this.system, attribute);
 		const current = isBar ? attr.value : attr;
 		const update = isDelta ? current + value : value;
@@ -36,18 +60,7 @@ export class TAFActor extends Actor {
 			return this;
 		};
 
-		// Determine the updates to make to the actor data
-		let updates;
-		if (isBar) {
-			updates = {[`system.${attribute}.value`]: Math.clamp(update, 0, attr.max)};
-		} else {
-			updates = {[`system.${attribute}`]: update};
-		};
-
-		// Allow a hook to override these changes
-		const allowed = Hooks.call(`modifyTokenAttribute`, {attribute, value, isDelta, isBar}, updates, this);
-
-		return allowed !== false ? this.update(updates) : this;
+		return super.modifyTokenAttribute(attribute, value, isDelta, isBar);
 	};
 	// #endregion Token Attributes
 
@@ -80,8 +93,15 @@ export class TAFActor extends Actor {
 	};
 	// #endregion Roll Data
 
-	// #region Getters
+	// #region Methods
 	#sortedTypes = null;
+	/**
+	 * @override
+	 * This override is intended to allow the "generic" item subtype to instead
+	 * populate the Item types based on their "Group" property, for any other item
+	 * subtype this function operates the same way that the default Foundry
+	 * implementation does.
+	 */
 	get itemTypes() {
 		if (this.#sortedTypes) { return this.#sortedTypes };
 		const types = {};
@@ -97,7 +117,29 @@ export class TAFActor extends Actor {
 		};
 		return this.#sortedTypes = types;
 	};
-	// #endregion Getters
+
+	/**
+	 * Retrieves an attribute Item from the actor, used to more easily
+	 *
+	 * @param {string} key The unique identifier of the attribute
+	 * @returns The attribute's Item document, or undefined if not found
+	 */
+	getAttribute(key) {
+		const attrs = this.itemTypes.attribute ?? [];
+		return attrs.find(attr => attr.system.key === key);
+	};
+
+	/**
+	 * Updates an embedded attribute Item with a new value.
+	 *
+	 * @param {string} key The unique identifier of the attribute
+	 * @param {number} value The value to set the attribute to
+	 */
+	async setAttributeValue(key, value) {
+		const item = this.getAttribute(key);
+		await item?.update({system: { value }});
+	};
+	// #endregion Methods
 
 	// #region Data Migration
 	/**

module/documents/Token.mjs

@@ -83,22 +83,12 @@ export class TAFTokenDocument extends TokenDocument {
 
 		if (`value` in data && `max` in data) {
 			let editable = hasProperty(system, `${attribute}.value`);
-			const isRange = getProperty(system, `${attribute}.isRange`);
-			if (isRange) {
-				return {
-					type: `bar`,
-					attribute,
-					value: parseInt(data.value || 0),
-					max: parseInt(data.max || 0),
-					editable,
-				};
-			} else {
-				return {
-					type: `value`,
-					attribute: `${attribute}.value`,
-					value: Number(data.value),
-					editable,
-				};
+			return {
+				type: `bar`,
+				attribute,
+				value: parseInt(data.value || 0),
+				max: parseInt(data.max || 0),
+				editable,
 			};
 		};